The present invention relates to a wave shaping circuit for wave shaping and amplifying a plurality of signals of different phases.
With recent use of large capacitive semiconductor memories charge coupled devices (CCD) have been increasingly used for memory devices. The CCD transfers electrical charges therein in response to application of clock signals with different phases to a plurality of CCD elements.
In the device, overlap capacitance formed among the electrodes receiving clock signals and electrode capacitance formed between electrodes and the reference potential point (ground), cause clock signals to interfere with one another, resulting in noise known as cross coupled voltage. The overlap capacitance and the electrode capacitance arise inherently from the structure of the CCD. Generally, in the case of large capacitive CCD, these capacitances are each approximately several hundreds pF so that the cross coupled voltage is necessarily produced.
When the cross coupled noise takes place in the clock pulses, undesirable active voltage is applied to electrodes other than the active electrode in the CCD operation. As a result, potential wells interfere with one another in charge transfer operation. More specifically, a high level signal is applied to the electrode of the CCD elements to be at low level so that the height of the barrier is lowered and thus charges stored in a potential well flow into adjacent potential wells. Thus, charges in those potential wells interfere each other in complex manner. This leads to reduction of the charge transfer efficiency and erroneous operation of the CCD.
In general, when active devices with capacitive structure included in the CCD are driven by multiphase clock signals, it is necessary to minimize the interference of the potential wells against the maximum cross coupled voltage produced in order to secure normal operation of such devices.